<!DOCTYPE html>
<html lang="zh-CN">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
</head>

<body>
  <script>
    class Father {
      constructor(x, y) {
        this.x = x;
        this.y = y;
      }
      sum() {
        console.log(this.x + this.y);
      }
    };
    class Son extends Father {
      constructor(x, y) {
        super(x, y) //调用了父类的构造函数

      }
    };
    let haha = new Son(10, 2);
    haha.sum();
  </script>
</body>

</html>